This invention relates to a method and apparatus for separately collecting the components of a sample separated by chromatography.
In a known method of collecting separated sample components by using a liquid chromatograph, the operation is controlled in accordance with a time schedule preset on the basis of the time: of sample injection and the retention times of the components of a sample in such a manner that collection is conducted for a period of time in which a sample component of interest is supposed to continuously elute from the chromatograph. Since the retention time of a sample varies with temperature, the kind of the mobile phase used, or the amount of the sample injected, a time lag is likely to occur between the collecting operation and the period of time during which the sample component to be collected elutes from the column of the chromatograph.
To enable accurate collection there have been proposed various methods, in one of which not only the time schedule indicating the periods of time during which the respective sample components are supposed to elute is relied upon, but also the rising edge of a peak on the chromatogram indicative of a sample component actually eluting is detected, or whether or not the output of the detector of the chromatograph exceeds a predetermined level is checked, so that collection of the sample component of interest is conducted upon confirmation of the actual elution of the sample component from the chromatographic column.
In another of the known methods, the retention time of a sample component from the time of injection of the sample as a starting point is not relied upon, but a specific peak, say, the first peak on the chromatogram is used as a starting point for the time schedule thereby to reduce the time lag between the retention time of a sample component of interest and the time of the collecting operation.
The above-mentioned prior art method, which uses not only the retention time of a sample component with the injection time of the sample as a starting point but also confirmation of the existence of the rising edge of a peak on the chromatogram or the level of the output of the detector of the chromatograph to conduct the operation of collecting the sample component of interest, is not useful when the retention time of a sample component to be collected differs so greatly from that preset in the time schedule that no peak is detected during the period of time in which a peak is expected to appear.
The prior art method, which uses a time schedule which starts at a specific peak on the chromatogram, is not adversely influenced by a lag in the retention time. Since collection is conducted only during a predetermined period of time upon lapse of a predetermined period of time after a specific peak on the chromatogram, the method cannot deal with variation of the amount of a sample component. If the amount of a sample component to be collected is large, the rising and descending end portions of the peak may not be collected. On the contrary, if the amount is small, a large amount of the mobile phase is collected thereby to reduce the concentration of the collected sample component.